Oysters and Carbonate Budgets in Estuaries

A pleistocene oyster reef exposed at low tide on the Piankatank River in Virginia. Note the depth of this geological deposit.Oysters are unusual among the approximately 8,000 species of bivalves in that they have foregone the typical infaunal habitat and the requisite burrowing foot, and lost one adductor muscle to adopt a sedentary, monomyarian, epifaunal, morphologically plastic, gregarious accreting (reef) form. Oysters reefs form the majority, if not the only vertically structured hard surfaces above the sediment-water interface in the majority of sedimentary estuaries in temperate and subtropical latitudes worldwide. As such their physical presence is central to the development of any community structure and associated food web requiring hard substrate. Reef formation rates and persistence dictates the rates of both primary invasion of ephemeral, over geological time, estuaries and subsequent development of estuarine communities with sea level rise. Emergent reefs reduced fetch associated with complex spatial heterogeneity based on those reefs and provide extensive inter reef environments sea grass beds and more abundant molluscan infauna. The degradation of shell carbonate above the sediment-water interface through taphonomic processes contributes to stable water chemistry, while the dissolution of buried shell buffers acid production from organic degradation below the interface, in doing so stabilizing the microenvironment and enabling perpetuation of the infaunal community. As a central factor in the carbonate budget of estuarine waters oysters are arguably pivotal in the response of resident communities to climate change. The rate processes controlling this entire suite of community development and food web processes are anchored in a quantitative understanding of the rates of individual and population processes for oysters.

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